What is a melanoma in situ?
A melanoma in situ is a lesion that can be regarded as the last stage before melanoma. Melanocytes (pigment cells) have already changed into melanoma cells, but these are all still confined to the upper layer of the skin (the epidermis). Only when these cells begin to extend into the deeper layer (the dermis) is there a true melanoma. Melanoma in situ is therefore generally considered “only” a precursor of skin cancer, and not an actual melanoma.
How does it look?
A melanoma in situ usually looks like an “irregular” mole — that is, a mole with an irregular border, several colours and asymmetric pigmentation. Sometimes the patient has noticed growth of the “mole”, but this is not always the case. A melanoma in situ that arises from a lentigo is also called a lentigo maligna. This form is seen mainly on the face, particularly in older patients.
What are melanocytes?
Normal melanocytes protect the skin against the harmful effects of sunlight. When melanocytes occur in clusters, visible pigment spots can appear — these are the spots we all know as moles. Like other cells in the body, melanocytes can change into cancer cells. This can happen both to melanocytes within moles and to melanocytes elsewhere in the skin.
What are the risk factors for melanoma in situ and melanoma?
- A fair skin type. People with a very fair skin type (who burn easily) have a greater risk of melanoma.
- Sunburn, particularly in childhood. Repeated sunburn, especially before the age of five, appears to increase the risk of developing melanoma later in life.
How is melanoma in situ treated?
For a spot suspicious of melanoma in situ, a dermatologist usually cannot rule out a true melanoma on clinical examination. The lesion is therefore always removed surgically at first, in the way that is usual for a melanoma — that is, with at least a few millimetres of healthy skin as a margin.
If pathological examination shows that the lesion is a melanoma in situ, the margin with which it was initially removed is reviewed. Guidance recommends that a melanoma in situ is removed with a clear margin of about 5 mm. Further treatment is not needed. If the patient has many atypical moles, a yearly check-up with the dermatologist is advised.
When to see a doctor
See a doctor for any mole that becomes irregular in shape, develops several colours, changes or grows — so that a melanoma in situ or melanoma can be assessed and removed early, when treatment is simplest and most effective.